In the last two decades the number of light-weight display devices has grown at a staggering rate. Examples of such light-weight display devices are e.g. mobile phones, personal digital assistants (PDAs), portable DVD players, and portable game consoles.
Such devices are often used in public places, quite often in the presence of others. As a result, the information presented on these display devices may become visible to others, e.g. to fellow passengers on a train or subway. In crowded public areas there is little privacy, and software and hardware features that can provide additional privacy are greatly appreciated by users of display devices.
Various solutions have been conceived to address this problem and to improve the privacy of such display devices, e.g. by means of a security film which is attached to the screen.
A disadvantage of the above solution is that having to apply and/or remove the film is undesirable. “Privacy LCD Technology for Cellullar Phones” by, Paul Glass et al, published in Sharp Technical Journal, No. 27, 2007, presents an alternative, switchable, solution which is suitable for mass manufacture. This paper proposes the use of an Electrically Controlled Birefringence (ECB) switch panel to provide additional privacy. When a small voltage is applied to the ECB switch panel, the liquid crystal tilts out of the plane of the glass panel. The plane in which the liquid crystal tilts remains parallel to the polarizers of the panel, therefore light propagating near the on-axis direction of the display is not affected by the switch panel. However, light propagating at a large angle to the on-axis direction has its plane of polarization rotated by the tilted liquid crystal layer. This light is then blocked by an additional polarizer, giving a dark view to the sides. Although switchable, the above solution requires an additional optical layer in the display panel.